1. Field of the Invention
The present invention relates to a method for manufacturing a center cap for use in a speaker (hereinafter referred to as a speaker-use center cap), and more particularly to a method for manufacturing a center cap for use in a speaker in a multi-layer structure including a first cap member layer of synthetic resin molded in a predetermined shape by injection molding and a second cap member layer (skin layer) layered or stacked in intimate contact on the first cap member layer and made of a different material from the first cap member layer.
2. Description of the Related Art
In an electrodynamic speaker, which produces sound through amplitude-vibration of a diaphragm by a magnetic circuit, an opening is formed at the center of the diaphragm to secure a cylindrical voice coil bobbin passed through a magnetic gap of the magnetic circuit.
In order to prevent invasion of an extraneous material such as dust from the opening at the center of the diaphragm into the magnetic gap, a center cap is put on the vicinity of the center of the diaphragm of the speaker so that it stops or closes the opening to which the voice coil bobbin is attached.
Since such a center cap is amplitude-driven integrally to the diaphragm, it is required to have various physical properties in order to prevent the acoustic vibrating characteristic of the diaphragm from being reduced.
Concretely, the center cap is required to have the is physical properties similar or identical to those of the diaphragm, i.e. large specific modulus (E/p) or specific bending modulus (E/p3), suitable internal loss, endurance to mechanical fatigue and good weatherability. Further, in recent years, moisture resistance is also an important property for mainly a vehicle application.
In order to satisfy these demands, as the material for the center cap, metal, ceramics, synthetic resin, synthetic fiber, and natural cellulose fiber have been proposed. In recent years, various raw materials such as a microbe cellulose fiber made by biotechnology have been also proposed. The materials thus proposed have been machined into a predetermined cap shape by various machining techniques.
However, each raw material has its own property. The raw materials proposed have merits and demerits from the standpoint of view of the physical property of the center cap.
Therefore it is actually difficult to cause the center cap formed of a single material to exhibit many physical properties required as the center cap in good balance.
For example, “paper center cap” using the cellulose fiber such as wooden pulp as the raw material is relatively right in weight, and has an appropriate elasticity and internal loss. The paper center cap presented merits of is being manufactured by various techniques and of high freedom of design, but presented demerits of difficulty of assuring the waterproof and of providing high elasticity to ensure high input endurance.
On the other hand, the synthetic-resin center cap or metallic center cap has merits of easiness of assuring the waterproof and of providing the high elasticity to ensure high input endurance, but demerits of a high density and small internal loss (although some resins have large internal loss). Therefore, the synthetic-resin center cap or metallic center cap is not optimum as the center cap put on the diaphragm for a low-to-midi range or all bands which requires light weight and high rigidity.
In view of the above circumstances, it has been proposed to provide the center cap with a good balance in the physical properties by adopting a multi-layer structure consisting of a plurality of raw materials with different physical properties to compensate for the demerits of the individual raw materials.
FIG. 1 shows an example of such a speaker-use center cap.
A speaker-use center cap 1 illustrated herein has a double layer structure consisting of a first cap member layer 3 made of synthetic resin molded in a predetermined shape by injection molding and a second cap member layer (skin layer) 5 layered in intimate contact on the first cap member layer 3 and made of a different material from the first cap member layer 3.
By compensating for the demerit of e.g. woven cloth of aramid fiber used as a raw material of the second cap member layer 5 by the characteristic of the resin layer, the center cap having various physical properties in good balance can be obtained.
Meanwhile, as a method for manufacturing such a speaker-use center cap 1 in a multi-layer structure, there has been proposed a method in which after the first cap member layer 3 and the second cap member layer 5 have been individually made, both layers are integrated using e.g. adhesive as required (e.g. see JP-A-2003-052100) or another method in which with the second cap member layer 5 having been previously molded in a predetermined size/shape by a separate press molding machine, the second cap member layer 5 thus molded is insert-molded in molding the first cap member layer 3 so that it is integrated to the first cap member layer 3 (e.g. see JP-A-7-111695).